WO2018184051A1

WO2018184051A1 - A nonwoven material designed for use in absorbent core structures with intrinsic acquistion/distribution capabilities

Info

Publication number: WO2018184051A1
Application number: PCT/AT2017/000032
Authority: WO
Inventors: Tom Carlyle; Mirko Einzmann; Gisela Goldhalm; Malcolm John Hayhurst; Katharina Mayer; Ibrahim SAGERER-FORIC
Original assignee: Lenzing Ag
Priority date: 2017-04-03
Filing date: 2017-04-03
Publication date: 2018-10-11

Abstract

This invention relates to an absorbent core structure comprising: (a) an essentially pure cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and/or physical intermingling of filaments, and (b) combined with superabsorbent polymer, for use in hygiene products. This product is thin, lightweight and flexible and has high wet and dry strength, excellent absorbency and retention, and maintains the superabsorbent polymer in its designed location, both dry and when wet and swollen. It further relates to the use of the inventive absorbent core structure according for the manufacture of a hygiene product. Further it relates to a hygiene product characterized in that it contains the inventive absorbent core structure, the use of the inventive absorbent core structure where it is combined with another nonwoven material to produce a nonwoven composite for hygiene applications and the use of the inventive absorbent core structure to provide the functions of acquisition/distribution layer, a core wrap and an absorbent core in a single hygiene product and/or structure.

Description

A nonwoven material designed for use in absorbent core structures with intrinsic acquisition/distribution capabilities

This invention relates to a thin, flexible absorbent core structure with intrinsic acquisition and distribution capabilities, and, more particularly, to an absorbent core composed of an essentially pure cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and physical intermingling of filaments, combined with superabsorbent polymers. This absorbent core is distinguished by its lack of fluff pulp as a component. This absorbent core is thin, flexible, absorbent with excellent liquid retention; the nonwoven web used is capable of acquiring and distributing the liquid to the absorbent polymer, as well as holding the absorbent polymer in position both dry and wet; used in a hygiene or personal care product, for example a baby diaper or feminine hygiene pad, this absorbent core reduces product weight, thickness, and shipping costs.

The term "essentially pure cellulose" shall address the fact that cellulosic moulded bodies, e.g. made according to the lyocell process, always contain a small amount of polymers other than cellulose, namely hemicellulose. This does not influence in any way the suitability for the use according to this invention.

Prior Art

Absorbent hygiene and personal care products including baby diapers, feminine hygiene pads, and adult incontinence products all contain an absorbent core to absorb and hold liquids. Most of these products also contain an acquisition/distribution layer, which rapidly pulls liquid from the surface (acquisition) and then moves this liquid both along the surface of the absorbent core as well as into the absorbent core itself. This maximizes surface dryness and utilization of as much as possible of the absorbent core. Finally, depending on the absorbent core structure, most products also contain a core wrap sheet, either tissue or nonwoven, to contain the

superabsorbent polymer powder, both during production of the core and during use of the hygiene or personal care product. In the mid 1980s, an absorbent core for hygiene and personal care products was developed which was a blend of fluff pulp and superabsorbent polymer powder. U.S. 5,147,343 and U.S. 5,599,335 teach the use of blended fluff pulp and superabsorbent polymer powder for use as an absorbent core.

In the late 2000s, the first "pulpless' absorbent cores were commercialized, in order to produce a thinner, lighter weight absorbent core. Many products attempt to optimize this type of core.

U.S. 8,260,533 teaches the use of thermoplastic adhesives, printed onto a nonwoven in a desired pattern, and adhering the superabsorbent polymer onto this pattern of adhesive. This pattern places the superabsorbent polymer powder in desired locations and keeps the powder separated so that liquid can reach most of the powder. Additionally, both when dry or wet and swollen, the powder is held in place. This core usually requires a separate special pulp containing acquisition/distribution layer.

WO 2012/052172 teaches the use ultrasonic bonding of two layers of nonwovens, forming pockets for the superabsorbent polymer powder to reside. These pockets hold the superabsorbent polymer powder, both when dry and when wet and swollen. These pockets allow enough space for the superabsorbent polymer powder to absorb and swell freely. This core usually requires a through air bonded nonwoven acquisition/distribution layer.

EP 1974705 teaches the use of adhesives to bond two nonwoven layers, forming hexagonal pockets to hold the superabsorbent polymer powder.

These adhesive bonds are designed to open up when the superabsorbent absorbs liquid and swells. This core usually requires a through air bonded nonwoven acquisition/distribution layer.

WO 2014/001487 teaches the use of a multilayer structure composed of a top nonwoven layer, a layer of superabsorbent polymer powder, an

acquisition/distribution layer, and another bottom layer of nonwoven. These layers are all ultrasonically bonded in a small point bond pattern. The superabsorbent polymer powder is actually forced into the pores of the acquisition/distribution layer, and is free to swell. The top and bottom nonwoven layers serve as a core and acquisition/distribution layer wrap. This patent teaches a unitary acquisition/distribution layer, absorbent core and core wrap structure.

WO 2006/075073 teaches the use of only special, fast absorbing

superabsorbent polymer powder, which is physically distributed more heavily near and around the liquid entry point.

U.S. 2013/012899 and 2014/0052089 describe an absorbent core composed of a top and bottom layer of nonwoven, between which are superabsorbent polymer and elastic/stretchable filaments to form regions for the

superabsorbent polymer powder to reside and swell.

U.S. 2014/291987 teaches the use of a nonwoven layer with pre-formed pockets, into which the superabsorbent polymer powder is dispensed, then covered with a standard nonwoven sheet; adhesives are used to bond the cover nonwoven to the pre-formed nonwoven.

WO 2013/153235 teaches the use of an absorbent core structure with an included acquisition/distribution layer. This core is composed of an open structure nonwoven with a pore size gradient such that superabsorbent polymer powder applied on top can be pulled into the nonwoven by vacuum or physical pressure. The pore size gradient allows coarser particle

superabsorbent polymer to stay on one side of the core, while the finer particles move to the other side of the core. The finer particles absorb more rapidly than the coarser particles, which absorb more liquid.

WO 2014/009506 describes an absorbent core structure with an included acquisition/distribution layer. This core is produced in one production process, and is composed of multiple layers of airlaid fluff pulp, one layer dense and having no included superabsorbent polymer, one layer having little fluff pulp, but most of the superabsorbent and another layer being open but having little superabsorbent. These multiple layers hold the superabsorbent polymer and perform as both the absorbent core and the

acquisition/distribution layers.

All of these products address some, but not all of the problems with absorbent cores. Blends of fluff pulp with superabsorbent polymer powder, as described in U.S. 5,147,343 and U.S. 5,599,335, are low cost and absorbent, but do not contain the superabsorbent polymer powder, either dry or wet, and do not easily place the superabsorbent polymer powder in desired locations, are not thin nor lightweight, and do require a separate acquisition/distribution layer.

Products using adhesive to hold and position the superabsorbent polymers, including those describe in U.S. 8,260,533, EP 1974705, and U.S.

2014/291987 all do restrict the swelling of the superabsorbent polymer and do reduce the usable superabsorbent polymer surface area, where the adhesive impinges the superabsorbent. They also require a separate

acquisition/distribution layer.

To eliminate the negative effects of adhesives, there are products, which substitute ultrasonic bonding for adhesive bonding, such as those described by WO 2012/052172 and WO 2014/001487. Ultrasonic bonding of such structures is a complex process, is slow and requires select nonwovens able to be ultrasonically bonded. Most polymers able to be ultrasonically bonded are thermoplastic and synthetic. These can interfere with absorbency of liquids.

Some products include acquisition/distribution capabilities within the core structure, such as those described in WO 2014/001487, WO 2013/153235, and WO 2014/009506. Unfortunately, the acquisition/distribution layer are either formed separately and added later in a complex process, or are compromise products which do not perform as well as separate

acquisition/distribution layers. There is still a need for an unitary absorbent core structure which performs as well as separate absorbent core, acquisition/distribution layer and core wrap, which holds the superabsorbent polymer in designed locations, both wet and dry, has high absorbency and retention of liquids, uses the superabsorbent polymer efficiently, and is thin, flexible and light weight.

Problem

Conventional absorbent products, such as those used in baby diapers, feminine hygiene pads and adult incontinence products, are usually composed of a liquid permeable topsheet, an acquisition/distribution layer, an absorbent core (including a sheet material as a "core wrap") and a liquid impermeable backsheet. Most current absorbent cores, where high absorbency is needed, are composed of fluff pulp and superabsorbent polymer. Superabsorbent polymer absorbs and holds many times its own weight in liquid, but it is slower to absorb this liquid than, for example, fluff pulp. Fluff pulp absorbs less fluid, but does so rapidly; unfortunately, fluff pulp releases fluids easily, especially under pressure, weight or load. Additionally, when superabsorbent absorbs liquids, it swells and forms a gel. If

superabsorbent polymer is used in high concentrations, it forms a mass of swollen particles, which can restrict movement of liquid to unused

superabsorbent polymer. Most current absorbent cores for hygiene and personal care products use a blend of fluff pulp and superabsorbent polymer to allow more utilization of the superabsorbent polymer and faster absorbency of liquids. A further modification of such products is the addition of an acquisition/distribution layer. An acquisition/distribution layer has a top surface with a function to rapidly acquire or absorb liquids and rapidly move them from the surface to the distribution layer. The distribution layer's purpose is to move liquid both to the absorbent core as well as in the x-y direction along the surface of the absorbent core. This maximizes usage of the absorbent surface area. Further, the distribution layer can hold some liquid as a buffer, while the superabsorbent polymer in the absorbent core more slowly absorbs and holds this liquid. The optimal performance of the hygiene or personal care product depends on the combined performance of the acquisition/distribution layer and the absorbent core. Current absorbent cores, as mentioned previously, are typically composed of fluff pulp and superabsorbent polymer. The superabsorbent polymer is supplied as a dry powder or granule material. When blended with fluff pulp, this powder can easily move within the core, both dry and when wet. Some powder can easily escape and is wasted. The dry powder, when it escapes during the processing and production of the product, can also present a health hazard to the production personnel. To minimize the escaping of

superabsorbent polymer powder, the entire fluff/superabsorbent polymer mixture is wrapped in a sheet material, either tissue or nonwoven. Tissue has very low strength especially when wet, but is low cost. Nonwovens have higher wet strength, but are more costly.

Another type of absorbent core has recently entered the market. This core does not use fluff pulp, but uses only or primarily superabsorbent polymer powder which has been adhesively adhered to a nonwoven sheet. This core does eliminate the need for a core wrap, but still requires an

acquisition/distribution layer.

For optimal performance of a hygiene or personal care absorbent product, that product must have an efficient acquisition and distribution layer, a fast, high liquid absorbent and high liquid retention core, and a core wrap, which holds in superabsorbent polymer powder without slowing transmission of liquids. Additionally, the core should use as much as possible of the included superabsorbent polymer.

It is desired that the hygiene or personal care article be as thin and lightweight as possible, while still meeting performance requirements. Additionally, it is desired that such a product be low cost and without excessive complicated process issues.

There is still a need for a low cost, lightweight, thin high liquid absorbing and retaining capabilities, which has a simple production process. Description

It is the object of the present invention to provide a thin, flexible absorbent core structure with intrinsic acquisition and distribution capabilities, and, more particularly, to provide an absorbent core structure comprising: (a) an essentially pure cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and/or physical intermingling of filaments, and (b) a superabsorbent polymer combined with the cellulose nonwoven web. This absorbent core is distinguished by its lack of fluff pulp as a component. This absorbent core is thin, lightweight and flexible and has high wet and dry strength, absorbent with excellent liquid retention; the nonwoven web used is capable of acquiring and distributing the liquid to the absorbent polymer, as well as holding the superabsorbent polymer in its designed position both dry and when wet and swollen.

Once having learned about the present invention, the skilled in the art may choose a suitable method, basically already known in the art, for combining the superabsorbent polymer with the cellulose nonwoven web. There are multiple methods for making the inventive absorbent core including, but not limited to: (a) the superabsorbent powder can be combined with the cellulose nonwoven web during the production of the web, (b) the superabsorbent powder can be combined with the cellulose nonwoven web in a secondary process after the manufacturing of the web and prior to the manufacturing of the hygiene product, (c) the superabsorbent powder and the cellulose nonwoven can be combined with other components after the manufacturing of the web and prior to the manufacturing of the hygiene product, and (d) the superabsorbent powder can be combined with the cellulose nonwoven web as part of the manufacturing process for the hygiene product.

Used in a hygiene or personal care product, for example a baby diaper or feminine hygiene pad, this absorbent core reduces product weight, thickness, and shipping costs. For concise description purposes, the term hygiene products shall be used to reference all baby diaper products, a women's feminine care pad product, a tampon product and/or any adult incontinence product, with the requirement that these products must be contain at least one component that includes at least one nonwoven material.

This material is designed to be a sustainable and cost effective nonwoven with good absorbency. It is clear that an essentially pure cellulosic material has better absorbent capacity and superior liquid management properties (liquid uptake, good spreadability and good wicking) than synthetic polymers such as polypropylene and polyester, which are typically used for the majority of hygiene components.

The inventive material is unique in that it used an essentially pure cellulosic nonwoven to provide the fluid distribution network for the fluid that enters the hygiene product. In general, absorbent cores are of limited strength, minimal distribution, good absorbency, and fair superabsorbent utilization, such as fluff pulp & superabsorbent powder cores, or they are of high strength, good distribution, minimal absorbency and good superabsorbent utilization. The inventive material, in a preferred embodiment, will have good strength, good distribution, good absorbency and good superabsorbent utilization. This combination of performance factors is not found in the absorbent core designs used today.

Preferably, the cellulosic nonwoven web is made according to a lyocell process.

Cellulosic fibres can be produced by various processes. In one embodiment a lyocell fibre is spun from cellulose dissolved in N-methyl morpholine N-oxide (NMMO) by a meltblown process, in principle known from e.g. EP 1093536 B1 , EP 2013390 B1 and EP 2212456 B1. Where the term meltblown is used it will be understood that it refers to a process that is similar or analogous to the process used for the production of synthetic thermoplastic fibres (filaments are extruded under pressure through nozzles and stretched to required degree by high velocity/high temperature extension air flowing substantially parallel to the filament direction), even though the cellulose is dissolved in solution (i.e. not a molten thermoplastic) and the spinning & air temperatures are only moderately elevated. Therefore the term "solution blown" may be even more appropriate here instead of the term "meltblown" which has already become somewhat common for these kinds of technologies. For the purposes of the present invention both terms can be used synonymously. In another embodiment the web is formed by a spun bonding process, where filaments are stretched via lower temperature air. In general, spunbonded synthetic fibres are longer than meltblown synthetic fibres which usually come in discrete shorter lengths. Fibres formed by the solution blown lyocell process can be continuous or discontinuous depending on process conditions such as extension air velocity, air pressure, air temperature, viscosity of the solution, cellulose molecular weight and distribution and combinations thereof.

In one embodiment for making a nonwoven web the fibres are contacted with a non-solvent such as water (or water/NMMO mixture) by spraying, after extrusion but before web formation. The fibres are subsequently taken up on a moving foraminous support to form a nonwoven web, washed and dried.

Freshly-extruded lyocell solution ('solvent spun', which will contain only, for example, 5-15% cellulose) behaves in a similar way to 'sticky' and deformable thermoplastic filaments. Causing the freshly-spun filaments to contact each other while still swollen with solvent and with a 'sticky' surface under even low pressure will cause merged filament bonding, where molecules from one filament mix irreversibly with molecules from a different filament. Once the solvent is removed and coagulation of filaments completed, this type of bonding is impossible.

It is another object of the present invention to provide a process for the manufacture of a nonwoven material consisting of essentially continuous cellulosic filaments by:

a. Preparation of a cellulose-containing spinning solution b. Extrusion of the spinning solution through at least one spinneret containing closely-spaced meltblown jet nozzles

c. Attenuation of the extruded spinning solution using high velocity air streams,

d. Forming of the web onto a moving surface [e.g. a perforated belt or drum], e. Washing of the formed web

f. Drying of the washed web

wherein in step c. and/or d. coagulation liquor, i.e. a liquid which is able to cause coagulation of the dissolved cellulose; in a lyocell process this preferably is water or a diluted solution of NMMO in water, is applied to control the merged filament bonding. The amount of merged filament bonding is directly dependent on the stage of coagulation of the filaments when the filaments come into contact. The earlier in the coagulation process that the filaments come into contact, the greater the degree of filament merging that is possible. Both placement of the coagulation liquor application and the speed at which the application liquor is applied can either increase, or decrease, the rate of coagulation. Which results in control of the degree (or amount) of merged filament bonding that occurs in the material.

Preferably the merged filament bonding is further controlled by filament spinning nozzle design and arrangement and the configuration and temperature of filament extension air. The degree of molecular alignment that is present as the solution exits the spinning nozzle has an impact on the coagulation rate. The more aligned the molecules are, the faster the coagulation rate, and conversely, the less aligned the molecules are, the slower the coagulation rate. The spinning nozzle design and arrangement, along with the molecular weight of the cellulosic raw material used will determine the starting coagulation rate at the exit of the spinning nozzle. Additionally, the rate of cooling (temperature decrease) of the solution upon spinning nozzle exit will impact the coagulation rate as well. The slower the cooling rate, the slower the coagulation rate, and conversely, the faster the cooling rate, the faster the coagulation rate. Therefore, configuration of the filament extension air can directing impact the cooling rate and therefore, impact the coagulation rate, which impacts the achievable amount of merged filament bonding that is possible.

In a preferred embodiment of the process according to the invention at least two spinnerets (also known as jets), preferably between two and ten, and further preferred between 2 and 6, each one arranged to form a layer of nonwoven web, are used to obtain a multilayer nonwoven material. By applying different process conditions at the individual spinnerets it is even possible to obtain a multilayer nonwoven material wherein the individual layers have different properties. This may be useful to optimize the nonwoven material according to the invention for different applications. In one

embodiment this could provide a gradient of filament diameters from one side of the material to the other side by having each individual web having a standard filament diameter that is less than the web on top, it is possible to create a material suitable for use as an air filter media that will provide a gradient of pore size (particle size capture). This will provide an efficient filtration process and result in a lower pressure drop across the filter media compared to a single web with similar characteristics at the same basis weight and pore size distribution.

Preferably the filaments are spun using a solution of cellulose in an aqueous amine oxide and the coagulation liquor is water, preferably with a content of amine oxide not being able to dissolve cellulose, also referred to as a lyocell process; the manufacture of such a solution is in principle known, e.g. from U.S. 6,358,461 , U.S. 7,067,444, U.S. 8,012,565, U.S. 8,191 ,214, U.S.

8,263,506 and U.S. 8,318,318; preferably the amine oxide is NMMO.

The present invention describes a cellulosic nonwoven web produced via a meltblown or spunbond-type process. The filaments produced are subjected to touching and/or compaction and/or intermingling at various points in the process, particularly before and during initial web formation. Contact between filaments where a high proportion of solvent is still present and the filaments are still swollen with said solvent causes merged filament bonding to occur. The amount of solvent present as well as temperature and contact pressure (for example resulting from extension air) controls the amount of this bonding. In particular the amount of filament intermingling and hydrogen bonding can be limited by the degree of merged filament bonding. This is the result of a decrease in filament surface area and a decrease in the degree of flexibility of the filaments. For instance, as the degree of merged filament bonding increase, the amount of overall surface area is decreased, and the ability of cellulose to form hydrogen bonds is directly dependent on the amount of hydroxyl groups present on the cellulosic surface. Additionally, filament intermingling happens as the filaments contact the forming belt. The filaments are traveling at a faster rate of speed than the forming belt. Therefore, as the filament contacts the belt, it will buckle and sway side to side, and back and forth, just above the forming belt. During this buckling and swaying, the filaments will intermingle with neighboring filaments. If the filaments touch and merge prior to the forming belt, this limits the number of neighboring filaments by which it can intermingle with. Additionally, filaments that merge prior to contacting the forming belt with not have the same degree of flexibility as a single filament and this will limit the total area over which the filament will buckle and sway.

Surprisingly, it has been found that high levels of control of filament merging can be achieved by modifying key process variables. In addition, physical intermingling of at least partially coagulated cellulose filaments can occur after initial contact with non-solvent, particularly at initial filament laydown to form the web. It arises from the potential of the essentially continuous filaments to move laterally during initial filament formation and initial laydown. Degree of physical intermingling is influenced by process conditions such as residual extension air velocity at the foraminous support (forming belt). It is completely different from the intermingling used in production of webs derived from cellulose staple fibers. For staple fibers, an additional process step such as calendaring is applied after the web has been formed. Filaments which still contain some residual solvent are weak, tender and prone to damage.

Therefore, in combination with controlling degree and type of bonding at this stage, it is essential that process conditions are not of a type which could cause filament and web damage. Initial drying of the washed but never-dried nonwoven, together with optionally compacting, will cause additional hydrogen bonding between filaments to develop. Modifying temperature, compacting pressure or moisture levels can control the degree of this hydrogen bonding. Such treatment has no effect on intermingling or the merged filament bonding.

In a preferred embodiment of the invention the nonwoven material is dried prior to subsequent bonding/treatment.

In a preferred embodiment of the invention the percentage of each type of bonding is controlled using a process with up to two compaction steps, where one of these compaction steps is done after step d. of the inventive process where the spun filaments are still swollen with a solvent, and one of these compaction steps is done before or in step e. of the inventive process where all or most of the solvent has been removed and the web has been wet with water. As previously discussed, control of the coagulation of the spun solution is a factor in controlling the degree of merged filament bonding. This preferred embodiment concerns decreasing the coagulation rate to a state where additional compaction steps can be used after filament laydown to further increase the actual amount of merged filament boding that is achievable. It might be helpful to view the maximum achievable filament bonding as the state where we have merged all filaments into an essentially film-like structure.

The present invention describes a process and product where merged filament bonding, physical intermingling and hydrogen bonding can be controlled independently. However, the degree of merged filament bonding can limit the degree of physical intermingling and hydrogen bonding that can occur. In addition, for the production of multi-layer web products, process conditions can be adjusted to optimise these bonding mechanisms between layers. This can include modifying ease of delamination of layers, if required.

In addition to merged filament, intermingling and hydrogen bonding being independently set as described above, additional bonding/treatment steps may optionally be added. These bonding/treatment steps may occur while the web is still wet with water, or dried (either fully or partially). These

bonding/treatment steps may add additional bonding and/or other web property modification. These other bonding/treatment steps include hydroentangling or spunlacing, needling or needlepunching, adhesive or chemically bonding. As will be familiar to those skilled in the art, various post- treatments to the web may also be applied to achieve specific product performance. By contrast, when post-treatments are not required, it is possible to apply finishes and other chemical treatments directly to the web of this invention during production which will not then be removed, as occurs with, for example, a post-treatment hydroentanglement step.

Varying the degree of merged filament bonding provides unique property characteristics for nonwoven cellulose webs with regards to softness, stiffness, dimensional stability and various other properties. Properties may also be modified by altering the degree of physical intermingling before and during initial web formation. It is also possible to influence hydrogen bonding, but the desired effect of this on web properties is minor. Additionally, properties can be adjusted further by including an additional

bonding/treatment step such as hydroentangling, needlepunching, adhesive bonding and/or chemical bonding. Each type of bonding/treatment provides benefits to the nonwoven web. For example, hydroentangling can add some strength and soften the web as well as potentially modifying bulk density; needling is typically employed for higher basis weights and used to provide additional strength; adhesive and chemical bonding can add both strength and surface treatments, like abrasive material, tackifiers, or even surface lubricants.

The present invention allows independent control of the key web bonding features: merged filaments, intermingling at web formation, hydrogen bonding and optional additional downstream processing. Manipulation of merged filament bonding can be varied to predominantly dictate the properties of the nonwoven web.

The nonwoven web preferably can be produced using a spunbond or solution blown die or head to form the continuous filaments, in principle known from the prior art cited above. Further teaching of how to produce the nonwoven web can be found e.g. in U.S. 6,358,461 , U.S. 7,067,444, U.S. 8,012,565, U.S. 8,191 ,214, U.S. 8,263,506 and U.S. 8,318,318 as well as in WO

98/26122, WO 99/47733, WO 98/07911 , US 6,197,230, WO 99/64649, WO 05/ 06085, EP 1 358 369, EP 2 013 390, WO 07/124521 A1 and WO

07/124522 A1 , the full content of those hereby incorporated by reference.

In a preferred embodiment of the invention, the nonwoven web is

hydroentangled. Undergoing this additional process enables a greater range of material functionality design. Such attributes as thickness, drape, softness, strength and aesthetic appearance can be tailored to meet specific consumer requirements.

Another object of the present invention is the use of the absorbent core structure according to the invention for the manufacture of a hygiene product. The inventive hygiene product due to elimination of the fluff pulp, and potential elimination of the acquisition / distribution layer, will have a thinner design which enables for a more sustainable product, supply chain and logistics. A thinner product results in either less packaging material being needed, less storage area needed, and less retail shelf space needed, or it enables that more individual hygiene products can be managed within the same space.

In a one embodiment of the inventive use, the inventive absorbent core can be combined with another nonwoven material to produce a nonwoven composite for hygiene applications. This can be done prior to the manufacturing of the final hygiene product, during the manufacture of the inventive absorbent core, or during a separate manufacturing process. This composite structure will enable topsheet functionality (fluid insult acquisition), ADL functionality (fluid absorption and wicking) and absorbent core functionality (fluid absorption, further wicking/distribution and fluid holding) to be maximized with a single composite design.

In another embodiment of the inventive use, the inventive absorbent core material is post treated with chemicals, polymers or other materials to modify absorbency, wicking, or other liquid handling properties. Such chemicals are well known to those experienced in the art. This embodiment allows for increased fluid management performance.

Still another object of the present invention is a hygiene product which contains an absorbent core structure according to the invention. The resulting hygiene product is able to provide the functions of acquisition/distribution layer, a core wrap and an absorbent core in a single structure.

In the embodiments discussed above, the inventive absorbent core design and/or multi-function composite structure may, or may not, be combined with a core wrap material in a single structure. The hygiene product is typically designed for a specific range of maximum fluid handling capability. For certain hygiene products, it may be preferred to use the inventive material with a core wrap such that a high level of superabsorbent powder may be better retained than with just the inventive absorbent core design itself.

Examples

All samples for testing were conditioned at 23°C ±2°C rel. humidity 50% ±5% for 24 hours.

Example 1

A unitary absorbent core structure of the current invention, composed of a 100% cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and physical intermingling of filaments, combined with superabsorbent polymers, and, in this example, the superabsorbent polymer is bonded to nonwoven with hot melt adhesives. Compared to this is a commercial product, which uses a thermal-bonded polypropylene nonwoven in place of the 100% cellulose nonwoven web of the current invention.

These samples were tested for tensile properties. Tensile properties were measured according to standard method DIN EN 29 073 part 3/ISO 9073-3, although a clamping length of 8cm rather than 20cm was used. The product of invention has 18 % more tensile strength in MD and 42 % more tensile strength in CD compared to the commercial product.

Example 2

A unitary core of the current invention is compared to major commercial and pre-commercial unitary cores. Table 1 below summarizes this comparison.

Absorbency was tested according to ISO 9073 - 6:2000. Thickness was measured according to ISO 9073 - 2:1995. Weight was measured using ISO 9073 - 1 :1989. Flexibility (stiffness) was measured using a 'Handle-o-meter', according to standard method WSP 90.3, with ¼ inch slot width, stainless steel surface, 1000 g beam. Sample size was to 10 x 10 cm.

The product of the current invention is at least equivalent to all of the competitive products in all attributes and is superior in required ADL cost as well as biodegradability. The eCore product has equivalent biodegradability, but requires a higher cost ADL and is thicker and heavier than the product of the current invention.

The product of the current invention has multiple bonding methods. It can be hydrogen bonded, hot melt adhesive bonded, or latex bonded, depending on needs.

Example 3

A 35-gsm product of invention was tested versus a commercial ADL product being comprised of soft carded thermal-bond coarse denier fibers, PP, permanently hydrophilic of same basis weight for its water uptake speed.

Water uptake was measured using an ATS (Absorbency Testing System ATS-600) . With that the test sample (sample size round, diameter 5 cm) is supplied with water from the bottom and water taken up by the sample without having any hydrostatic pressure is evaluated. The measurement for each sample was stopped after 1800 seconds. Figure 1 shows water uptake speed, average of 5 measurements.

Sample 1 (product of invention) versus sample 2 (commercial ADL product, soft carded thermal-bond coarse denier fibers, PP, permanently hydrophilic).

Figure 1 illustrates that only the product of invention was taking up water even though the competitive product was hydrophilized PP.

The same two samples of example 1 were further tested for their spreadability of liquid.

The test method was as follows.

0.5 ml of test liquid (water with 2g/L dye Sulfacide brilliant green) was pipetted onto each sample using an Eppendorf pipette. After 5 min, a picture of the liquid spread was taken and software (lmageJ1.49v, National Institute of Health, USA) used to evaluate the area of the liquid spread.

The product of invention showed a 2.7 fold higher area in spread liquid compared to the commercial ADL product.

The example shows that the product of invention has the ability to take up liquid fast and to spread it, even higher than a competitive ADL product. It is therefore showing high performance in transporting liquid to the super absorber and distributing it within the layer to equally supply liquid to all super absorber within the absorbent product.

Unitary Core Structures Absorbency Strength Bonding Thickness Weight Flexibility ADLcost Biodegradability

Current invention + + Multiple + + + Low

DryMax core (Procter & Gamble) + + Hot Melt + + + High¹

Drylock core (Drylock) + + Ultrasonic + + + High²

Hexacore core (Fameccanica) + + Hot Melt + + + High²

Helixbond core (Hermann Ultrasonics) + + Ultrasonic + + + Medium

Pulpless core (DSG) + + Hot Melt + + + High²

Evonik core (Evonik) + + Thermal 0 0 + High²

BASF/Bostik core (BASF/Bostik) + + Hot Melt + + + High²

eCore (Glatfelter) + + Thermal/Latex 0 0 + Medium

Scale: + best

0 moderate

- worse

Notes: 1 modified cellulose fibres + adhesive bonded polyester nonwoven

2 high basis weight through air bonded carded bicomponent/polyester nonwoven

Claims

1. An absorbent core structure comprising: (a) an essentially pure cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and/or physical intermingling of filaments, and (b) a quantity of superabsorbent polymer combined with the cellulose nonwoven web.

2. The absorbent core structure of claim 1 where the cellulosic nonwoven web is made according to a lyocell process.

3. The absorbent core structure of claim 1 where the nonwoven web is hydroentangled.

4. Use of an absorbent core structure according to claim 1 for the manufacture of a hygiene product.

5. Use of an absorbent core structure according to Claim 4 where the absorbent core structure according to Claim 1 is combined with another nonwoven material to produce a nonwoven composite for hygiene applications.

6. Use of an absorbent core structure according to Claim 4 or 5 where the absorbent core structure or the nonwoven composite is post treated with chemicals, polymers or other materials to modify absorbency, wicking, or other liquid handling properties.

7. A hygiene product characterized in that it contains an absorbent core structure according to claim 1.